Method of screw connecting carbon or graphite electrodes



May 30, 1967 I KOZIOL ETAL 3,322,

METHOD OF SCREW CONNECTING CARBON 0R GRAPHITE ELECTRODES Filed July. 30, 1964 2 Shets-Sheet 1 METHOD OF SCREW CONNECTING CARBON OR GRAPHITE ELECTRODES Filed July so, 1964 2 Sheets-Sheet 2 VVKYKOZIOL. ETAL 3,322,446-

United States Patent O C ,7 18 Claims. (Cl. 287-427) The present invention relates to screw connections between carbon or graphite electrodes. The generally cust-omary way of interconnecting carbon or graphite electrodes by means of screw nipples or studs has the drawback that the connecting sections easily become loosened by vibrations occurring in the furnace. Various electrode connections have become known which intend to prevent the said loosening. Some of these suggestions have gained acceptance in industry inasmuch as they have proved useful. However, these known electrode connections cause other difficulties which varyas to their magnitude, depending on the dimensions of the electrodes, the furnace types, fields of employment, methods of operation, and working conditions.

Thus, for instance, all methods based on a rigid cementing of the nipple in the electrode thread boxes have proved disadvantageous for the following reason. The stronger, i.e. the more rigid the connection is made between the nipple and the electrodes, the greater will be the danger that the electrode thread box burst in view of the mechanical shocks of the melt or in view of other vibrations of the furnace.

Furthermore, it has been found that in view of the frequently considerable temperature differences occurring at the connections between the upper and the lower electrodes during the operation of the furnace, it is necessary to provide the possibility of an expansion between the electrode thread and the nipple thread in order to obviate inadmissible heat tensions which may cause breaks at the connection between the electrode and the nipple thread. The assurance of a good screw connection must under no circumstances reduce or eliminate the desired play between the threads. This last-mentioned requirement could not be met heretofore by any methods of establishing a screw connection between carbon or graphite electrodes, according to which said connection was effected by means of known liquid or paste-like cements.

All of these methods have the drawback that in spite of very careful introduction of the cement substance, the latter distributes itself more or less in a random manner in the chambers, bores, gaps, passages, or the like, and passes between the thread turns of the nipple and of the boxes. All heretofore known heat hardenable electrode cements will, when heated, considerably reduce their viscosity and be transformed into a thin liquid substance and while swelling, expand and randomly wet the surfaces. It is only after passing through this phase that these cements when being subjected to further heat, will thicken, solidify, crack and finally coke. The time period over which this conversion process extends is dependent on the temperature conditions prevailing at the connection and also on the type and composition of the cement.

When employing the known tar pins, the same drawbacks referred to above will be encountered. In addition thereto, with the employment of said pins, an electrode connection sufficiently safe against becoming loosened will occur only after the tar has passed into coke condition,

- which, however, occurs only at relatively high temperatures.

To secure the connections by means of carbon pins which are driven laterally through the electrode boxes into bored holes in the nipple, has not proved reliable.

Experience has shown that due to the tensions caused by the carbon pin which is under high load, tears will occur in the electrode boxes whereby a loosening of the thread sections is unavoidable.

It is, therefore, an object of the present invention to provide an electrode connection which will be reliably secured against accidentally becoming loosened.

It is another object of this invention to provide an electrode connection as set forth in the preceding paragraph which will have the advantages of a screw nipple or stud while avoiding any of the above-mentioned difficulties.

A still further object of this invention consists in the provision of an electrode connection which is simple, safe against faulty handling, and can be produced at low cost.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing, in which:

FIGURE 1 shows a screw connection according to the present invention directly after the nipple has been screwed into the electrode, and prior to the employment of heat.

FIGURE 2 illustrates the conditions after the connection has been subjected to heat.

FIGURE 3 illustrates another embodyment of the invention.

The method of making screw connections between carbon and graphite electrodes, according to the present invention, is characterized primarily in that for purposes of preventing accidental loosening of the connection, blanks, preferably cylindrical pressed bodies, are employed which are composed of from 20 to 95% by weight of a difiiculty fusible, swellable, heat hardenable and cokable resin, preferably phenol-novolak-hexamethylene tetramine resin and from 5 to .by weight of filling material as, for instance graphite, coke, and/or silicon carbide. These pressed bodies are pressed into or cemented to bores or recesses of the nipple, stud, or electrodes after said bores have been lined with a thin insulating layer, for instance, of paper.

Depending on the respective electrode connection, generally two, or if necessary, more blanks are employed. The placing of said blanks may be effected at different points within the range of the electrode connection. According to a preferred manner, the said blanks are placed in bores which radially extend into the thread zone of the nipple. Another preferred place for said :blanks is the end face of the electrode to be connected with the nipple. In this instance, the blanks may be located in bores parallel to the longitudinal axis of the electrode' During the heating up of the screwed together electrode connection, the blanks become plastic, gradually start swelling, and greatly increase their volume without flowing away, and final'ly, depending on their location, contact the adjacent electrode box wall or the end face of the adjacent electrode and, so-to-speak, throw roots without being'subjected to stresses and soon thereafter, harden and coke in view of further being heated up. Thus, each blank is converted into a stable latch which is intimately fused with a portion of the electrode connection while simultaneously firmly engaging the bore of the other part without, however, adhering thereto in view of the insulation or lining in the bore. In the other words, the portion in the bore retains a certain play.

An electrode screw. connection with a blank according to the present invention thus automatically secures itself against loosening during the employment of said blank. An electrode connection according to the present invention excels. in an early ruggedness and a very good late ruggedness. The interlock created in this way does not exert an undue pressure upon the interconnected part but acts elastically. The desired thread play of the threaded connection is maintained without change, and the possibility of expansion of the interconnected parts is in no way aifected. An electrode connection in which the blanks are located in the end face of the electrode to be provided with a nipple has the additional advantage that if the screw connection should break, the nipple can be removed from the electrode bores without difficulties, and the non-damaged parts can again be employed without expensive and time-consuming post-working.

The blanks employed according to the present invention may easily be produced in numerous ways. According to a preferred method, a blank is form-pressed of a mixture, homogenized in a dry mixer, of from 20 to 95% by weight of a resin, preferably phenol-novolak-hexamethylene tetramine resin which has been ground to a finest grain and a difliculty fusible, swellable, heat hardenable, and cokable, and from to 80% by weight of finest ground fillers as, for instance, graphite, coke, and/ or silicon carbide. If desired, the blanks consisting of a homogenized and kneaded mixture of the above composition may be wetted with a dissolving intermediary as, for instance, spirits, and may be finish-formed only in the bores or recesses intended therefor and provided in the nipple stud or the electrodes.

Furthermore, if desired, gas separating propellents as, for instance, porofor, and plasticizing substances as, for instance, finely ground pitch, may be added to the pressed kneaded mixture. The adhesiveness of the blanks may, if necessary, be increased by coating their free end surfaces with a viscous resin as, for instance, phenol-resol or a layer of pitch.

An important advantage of the blanks according to the present invention consists in that they can be stored for many years, even at increased room temperature, without their quality being changed in any way.

Referring now to the attached drawing, FIG. 1 shows .the screw connection immediately after the nipple a has been screwed into the electrode box b while the blank c has not yet started to swell, and the insulating layer d still exists.

FIG. 2 illustrates how the blank c located in a bore or recess after the connection has been heated up, has greatly increased its volume and, so-to-speak, has thrown roots into the threads of the electrode box b while, due to the coking of the insulating layer and the thus created space e, the blank 0 has a certain play in the bore or recess 1. I

FIG. 3 illustrates an electrode connection by means of a screw-type nipple a after the initial heating process, whereby the blanks c located in the head surfaces of the electrode b to be joined have already thrown roots in the surface of the lower electrode g, the blanks thereby having a certain play e on account of the gap resulting from the coking of the insulating layer.

There will now be set forth some examples for the production of the blanks.

Example I A mixture, consisting to 50% by weight of a common grade phenol-novolak-hexamethy lene-tetramine resin having a particle size 70;], 30% by weight of silicone carbide, particle size below 45,u, and 20% by weight of graphite powder, particle size below 75 is homogenized for 15 minutes in a dry mixer at room temperature. The dry, compressable powder mix is subsequently fed into a fully automatically tablet machine which produces the finished blanks with the aid of a cold pressing tool. The pressure required for this operation amounts to 1.8 t./cm

Example II The basic composition of the powder mix is the same as quoted for example I. The powders are premixed for minutes at room temperature in a strong kneading machine. Subsequently and with the kneading machine running, 15% by weight of methanol are added. The kneading process then lasts for another 15 minutes. The tenacious plastic mass thus obtained is pressed in to the bores respectively recesses of the nipple, stud or electrode provided for the mass.

The term porofor according to column 3 of the description refers to the gas-splitting propellent consisting of benzol-sulfohydrazid.

It is, of course, to be understood, that the present invention is, by no means, limited to the particular method and embodiment set forth above, but also comprises any modifications within the scope of the appended claims.

Thus, while according to the drawing only one recess 1 has been provided in the element a, it is also possible to provide more than one recess therein. Furthermore, if desired, one recess 1 may be provided in the element a and another recess 1 may be provided in the element b. Corresponding pressed bodies c will then be inserted into said recesses.

What we claim is:

1. In a method of making screw connections between carbon electrode elements and also between electrode elements of graphite, the steps of: providing at least one of the elements to be screwed together with a recess; inserting into said recess a pressed body adapted not to flow at the temperatures occurring in said electrodes, said body comprising from 20 to 95% by weight of a difiiculty fusible, swellable, heat-hardenable, and cokable resin and also comprising from 5 to by weight of filler substance; securing said inserted body in said recess; and screwing together the electrode elements to be interconnected.

2. In a method of making screw connections between carbon electrode elements and also between electrode elements of graphite, the steps of: providing at least one of the elements to be screwed together with a recess; inser-ting into said recess a pressed body adapted not to fiow at the temperatures occurring in said electrodes, said body consisting of from 20 to by weight of difficulty fusible, swellable, heat hardenable, and cokable resin and of from 5 to 80% by weight of filler substance selected from the group consisting of graphite, coke, and silicon carbide; screwing together the electrode elements to be interconnected; and subjecting the inserted body to heat to thereby cause the same to swell and to prevent the screwed-together elements from getting loose.

3. A method according to claim 1, in which said resin is a phenol-novolak-hexamethylene tetramine resin.

4. A method according to claim 1, in Which said inserted body is pressed into said recess.

5. A method according to claim 1, in which said inserted body is cemented to the walls of said recess.

6. In a method of making screw connections between carbon electrode elements and also between electrode elements of graphite, the steps of: providing at least one of the elements to be screwed together with a recess; covering the inner wall surface of said recess with a thin lining of insulating material; inserting into the thus lined recess a pressed body adapted not to flow at the temperatures occurring in said electrodes, said body consisting of from 20 to 95% by weight of a difficulty fusible, swellable, heat-hardenable, and cokable resin and of from 5 to 80% by weight of filler substance selected from the group consisting of graphite, coke, and silicon carbide; screwing together the electrode element to be interconnected; and subjecting the inserted body to heat to thereby cause the same to swell and prevent the screwedtogether elements from getting loose.

7. A method according to claim 6, in whichsaid lining consists of paper.

8. A method according to claim 2, in which the material from which the pressed body is made contains a dissolving intermediary and receives its final shape in said recess.

9. A method according to claim 8, in which the spirit is employed as dissolving intermediary.

10. As a new article of manufacture: a body for securing threadedly interengaging electrode elements against loosening, especially of carbon, and of graphite, which comprises from 20 to 95% by weight of a difficulty fusible, swellable, heat-hardenable, and cokable resin and of from 5 to 80% by weight of filler substance selected from the group consisting of graphite, coke, and silicon carbide.

11. An article according to claim 10, in which said body comprises a dissolving intermediary.

12. An article according to claim 10, in which said body comprises a gas-separating propellent.

13. An article according to claim 10, in which said body comprises a porofor.

14. An article according to claim 10, in which said body comprises a plasticizing substance.

15. An article according to claim 10, in which said body comprises a finely ground pitch.

16. An article according to claim 10, in which the free end surface of the body is coated with a viscous resin.

17. An article according to claim 10, in which the free end surface of the body is co-ated with phenolresol.

18. An article according to claim 10, in which the free end surface of the body is coated with a layer of pitch.

References Cited UNITED STATES PATENTS 2,017,943 10/1935 Boughton 264-317 XR 2,421,105 5/ 1947 Warren.

2,836,806 5/1958 Stroup 174-94 XR 2,907,972 10/ 1959 Schildhauer et al. 252516 XR 3,003,975 10/1961 Louis 252-511 XR 3,076,050 1/ 1963 Hinckley 264-105 XR 3,081,269 3/1963 Shannon et al. 260-826 XR 3,121,129 2/1964 Knowlton 264- 3,187,089 6/1965 Cosby et al 174-94 ROBERT F. WHITE, Primary Examiner. T. I. CARVIS, Assistant Examiner. 

10. AS A NEW ARTICLE OF MANUFACTURE: A BODY FOR SECURING THREADEDLY INTERENGAGING ELECTRODE ELEMENTS AGAINST LOOSENING, ESPECIALLY OF CARBON, AND OF GRAPHITE WHICH COMPRISES FROM 20 TO 95% BY WEIGHT OF A DIFFLICULTY FUSIBLE, SWELLABLE, HEAT-HARDENABLE, AND COKABLE RESIN AND OF FROM 5 TO 80% BY WEIGHT OF FILLER SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF GRAPHITE, COKE, AND SILICON CARBIDE. 